1. Field of the Invention
This invention relates to housings provided with safety means thereon to relieve excessive pressure build-up within the housings, and has particular, though not exclusive, application to housings containing high voltage electric circuit re-closers.
2. Description of Related Art
Re-closers for high voltage electricity supply systems commonly comprise automatic and/or manually-operated circuit breakers located within sealed housings containing any one of a number of different fluids such as SF.sub.6 gas, oil and the like. Alternatively the housings may be evacuated.
Fault currents and voltages within these housings may be extremely high, typically several thousand amps and volts.
If an abnormal condition should arise whereby the operational capability of the equipment is impaired, inadvertent and undesirable electric arcing may occur within the housing.
The consequential temperature and pressure rises within the housing resulting from this undesirable arcing may be so high that disruptive failure of the housing can occur.
It would therefore be desirable to be able to incorporate pressure relief means on the housing to permit venting thereof once the pressure therein exceeded a predetermined critical value.
Currently available pressure relief devices typically comprise bursting discs. However, certain of these discs suffer from certain disadvantages, such as they have to be mounted in associated holders which, in turn, have to be mounted on the housing to be protected, they require periodic checking to determine the condition thereof, they can be prone to corrosion if located in a hostile environment, they can be prone to leakage and, in order to ensure adequate venting of large vessels containing high pressure fluid, they must be of relatively large area.